Optical disks are classified into recordable optical disks, e.g., DVD-Rs, and read-only optical disks, e.g., DVD-ROMs. For a DVD-R, tracking control is performed on the basis of a tracking error (push-pull TE) signal in the push-pull method, which is derived from a difference between reflected light from a guide groove (groove) of an optical disk. On the other hand, for a DVD-ROM, tracking control is performed on the basis of a tracking error (phase difference TE) signal in the phase difference method, which is derived based on a light beam spot and a time difference in passing through pits (physical protrusions and depressions: emboss pits). When a phase difference TE signal is employed, stable tracking control is achieved even when a lens shift or defocusing occurs.
In a conventional optical disk apparatus, it is necessary to determine whether a mounted optical disk is a read-only optical disk such as a DVD-ROM, or a recordable optical disk such as a DVD-R, and switch the tracking control method based on the result of determination. A method of determination by an optical disk apparatus between a recordable optical disk and a read-only optical disk is disclosed in Patent Document 1, for example.
On a read-only optical disk such as a DVD-ROM, data is recorded in the form of pits, and there is no guide groove that wobbles with a predetermined frequency or phase to record information. On the other hand, on a recordable optical disk such as a DVD-R, there is a guide groove that wobbles with a predetermined frequency or phase. Therefore, when a reproduction signal (RF signal) is generated from such a recordable optical disk, the reproduction signal will contain a signal (wobble signal) which is in accordance with the wobble of the guide groove. If a wobble signal can be extracted from a reproduction signal of an optical disk, it can be determined that the optical disk is not a DVD-ROM.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2002-133656